Note 3 - Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Net income	$ 15,190	$ 13,546	$ 13,702	$ 10,331	$ 28,736	$ 24,033
Basic earnings per common share - weighted-average shares (in shares)	54,616		54,613		54,585	54,592
Effect of dilutive stock options (in shares)	465		513		470	523
Diluted earnings per common share - weighted-average shares and assumed conversions (in shares)	55,081		55,126		55,055	55,115
Basic earnings per common share (in dollars per share)	$ 0.28		$ 0.25		$ 0.53	$ 0.44
Diluted earnings per common share (in dollars per share)	$ 0.28		$ 0.25		$ 0.52	$ 0.44